1. Field of the Invention
This invention relates to a method of manufacturing print hammers of the type employed in dot matrix printers. More particularly, the present invention relates to print hammers having an impact pin secured to a body. The body may be of the flat spring type. In printers employing such hammers, the spring is flexed to a stressed position by means of a permanent magnet and is released by applying a pulse to an electromagnet which overcomes the force of the permanent magnet. The spring will fly forward and the tip of the impact pin contacts an inked ribbon to cause a dot to be printed on a printing medium.
Typically, a number of flat spring print hammers (e.g., sixteen) are used in a print head. The print hammers are positioned so that the impact pins lie along a line and are spaced apart by a predetermined distance. In order to achieve high quality print, the impact tips must be precisely positioned with respect to one another. Errors in location of a few ten-thousandths of an inch can have a significant effect on print quality.
In addition to the requirement that the impact tips be precisely located with respect to each other, both the size of the impact tip (i.e., the diameter of the impact tip) and the distance of the impact tip from the mounting surface of the head (the surface where the head is mounted to the printer) are critical. The impact tip configuration is important to achieve the desired dot size. The distance from the impact tip to the mounting surface is important to ensure that a precise distance between the impact tip and the printing medium is maintained, thus providing the proper amount of printing energy for high print quality.
2. Description of the Prior Art
In prior art printers, the impact pin is machined or otherwise formed into the desired shape and then subsequently attached to the flat hammer spring by one of a variety of processes, such as resistance welding or press fitting. The tip of the impact pin is then ground to achieve a desired height with respect to the flat spring. Various hammer and impact pin configurations are disclosed in U.S. Pat. Nos. 3,941,051 to Barrus, et al. and 4,304,495 to Wada, et al. In both of these patents, the hammers are formed by initially forming the impact pin into its desired configuration and subsequently securing the impact pin to the flat spring. In order to achieve high print quality, the position of the impact pin on the spring must be precisely determined. In addition, the springs must then be mounted in the printhead assembly with extremely high precision in order to achieve the proper spacing between the impact pins of the various hammers. Since the impact tip is ground in relation to the spring, a precise relation must be maintained between the spring mount and the head mounting surface.